In isotope separation where an environment of uranium hexafluoride molecules is to be enriched in a selected uranium isotope by selectively photoexciting molecules having that isotope, it is frequently desirable to employ 16 micron radiation, appropriately tuned to selectively photoexcite the molecules with the desired atoms. While lasers exist capable of generating 16 micron radiation for this purpose, such as the TEA CO.sub.2 /SF.sub.6 laser, or the gas dynamic CO.sub.2 laser, or the hydrogen bromide pumped CO.sub.2 laser, greater efficiency is desired, paricularly in operating on the 02.degree.0 to 01'0 transition.
A difficulty which is encountered in such lasers is the loss of an inversion between the two levels separated by 16 microns of energy. This results in the premature cessation of laser radiation when the 01'0 level reaches some population level equal to that of the 02.degree.0 level.
In addition, prior schemes have been inefficient not only in the actual output power generated from the CO.sub.2 laser at 16 microns, but also in the utilization of pumping energy. In the case of pumping by optical means from an excitation laser, this is particularly wasteful in that the laser radiation employed for excitation is normally relatively expensive per photon. On the other hand, other pumping techniques such as found in the gas dynamic laser or electric discharge excitation, tend to be unselective, populating a whole succession of levels, thereby preventing the necessary population inversion between the 02.degree.0 and 01'0 levels necessary for 16 micron radiation. Since the 01'0 level has a long lifetime, over one second, continuous pulsed operation of the laser for any appreciable pulse duration is inhibited by a terminal block at the 01'0 level.